Electrical feedthroughs provide an electrical circuit path extending through a sealed container, such as a housing of an implantable medical device (IMD). Electrical feedthroughs include a conductive feedthrough pin that is electrically insulated from the container. In some examples, a feedthrough includes a ferrule and an insulator such as a hermetic glass or ceramic seal that supports the feedthrough pin within the ferrule.
Electrical feedthroughs for IMDs may be used in electrical medical devices such as electrical stimulators including neurostimulators and cardiac stimulators. Such electrical medical devices can be susceptible to electromagnetic interference (EMI). At certain frequencies, for example, EMI can inhibit stimulation signals from an electrical stimulator, such as pacing signals. For this reason, electrical feedthroughs may include a capacitor to shunt high frequency EMI from the feedthrough pin. In some examples, a capacitor is included within the ferrule such that the capacitor electrically contacts the feedthrough pin and the ferrule to shunt high frequency EMI away from the feedthrough pin.
In operation, a feedthrough capacitor permits passage of relatively low frequency electrical signals along the feedthrough pin, while shunting and shielding undesired high frequency interference signals to the ferrule, which may be physically and electrically coupled to a conductive housing of the device. Shunting high frequency interference signals away from the feedthrough pin mitigates the effects of EMI on a device by filtering high frequency signals from the feedthrough pin before the signals enter the interior of the device. This can limit adverse effects of EMI on the operations of an IMD, such as sensing, neurostimulation and/or cardiac stimulation therapy.